Watering Vegetable Gardens

Water provides more than just liquid to a plant; it’s also the medium that enables nutrients and minerals to enter the roots. (Roots don’t digest dirt — they’re not “woody earthworms” — but instead obtain their nutrients only in solution.) What’s more, through the process of photosynthesis, some of water’s hydrogen is split off to become a constituent of the carbohydrate compounds that make up most of the body tissue of growing plants.

Interestingly, water also enables plant roots to obtain nutrients that are beyond their physical reach. At varying depths below our feet lies the water table. Above that is soil containing minute, air-filled vestibules. When enough moisture surrounds each soil particle to create a continuous film from roots to water table, plants can, by capillary action, draw water and thus food from places far beneath their roots. (When this happens, the soil is said to have reached field capacity.)

If, on hot summer days, the crops use more water than is replaced, dry air spaces are created within the soil, and the bridge to the water table is broken. Conversely, if a real downpour hits and the air spaces become flooded to the point of excluding oxygen altogether, plants can literally drown — because roots must have air available, as well as water.

Whether or not your garden soil will retain water well without becoming over-saturated is determined, for the most part, by its structure. But don’t feel that you must live with the type of soil that’s currently in your plot. The great equalizer, compost, can help improve any ground that has trouble properly absorbing or retaining water.

Take sandy soils, for instance. They often have large spaces between their particles that allow for excellent drainage — if there is existing moisture in the soil. If, however, as might be the case in an extremely sandy soil, those spaces are completely filled with air, they can actually become a barrier to water penetration. Rain will be able to penetrate no deeper than the first few inches, so even though the garden has gotten a good soaking, deeper levels will remain bone-dry. When that happens, plant roots tend to seek out only the upper few inches of soil and will thus be quite susceptible to heat and moisture loss.

Compost added to such a sandy soil will act as a moisture-retaining wick. It should be incorporated deeply — say, six to eight inches — so it will also help attract roots downward.

Silty soil acts in much the same way. Its powdery, flour-like texture can let water slip right through . . . just as the soil itself would sift through your open fingers. In the process, that water will quickly leach nutrients from your plants. Here again, compost will give your plot a better water retaining capacity.

Clay soils have another problem: They have so few air spaces that they’re too easily flooded by water. A sticky, slimy, wet clay soil can easily drown roots. The addition of as much organic matter as possible is a definite must in order to lighten the soil to allow plant roots more room to breathe. At the Eco-Village, we turn in at least an inch of compost (and preferably more) before planting any crop in our clay-heavy beds.

Turning under green manure (or cover) crops is often another good way to add more humus to the soil. Our own clay plot, however, doesn’t have sufficient below ground air to stimulate the needed decomposition of turned-under crops, so we actually cut down most of the green matter and compost it before working it in.

On the other hand, adding sand to clayey soil is not supposed to help its texture — the clay allegedly “swallows” it up! As an old gardening maxim puts it: Put clay in sand, money in the hand; put sand in clay, throw money away. But when we finally tested this adage last summer by working about an inch of sharp creek sand into a few beds along with their compost allotment, the sand did make a noticeable improvement in both texture and drainage.

When to Water the Garden

Early mornings and evenings are almost magical times in every garden. The low rays of the sun impart a certain aura to leaves and fruit that’s lacking in the harsh light and heat of midday. And, as chance would have it, those are also the best times of day to water.

Here at the Eco-Village, we water our established beds a few hours before dusk, when the day’s work is behind us and the tranquility of early evening is descending. The soil, heated throughout the day, will warm the water as it percolates downward, making the liquid less chilling (and stressful) to the plants. Furthermore, watering in the early evening allows time for the foliage to dry before nightfall — preventing the sustained dampness that favors the spread of fungi and mildews. In addition, plants do much of their actual growing at night (employing the stored products of photosynthesis), so they can well use a late-day boost to their aqueous reserves. And evening is generally a time of reduced wind and cooler temperatures — so water added then will be less likely to evaporate (an important conservation consideration).

Of course, if you find that you spend most of your time in the garden during morning hours, you can water then instead. While doing so may not provide quite as many advantages as does early-evening watering, at least it avoids the hazards of adding water in the heat of the day (which can seriously stress plants) or at nightfall (which encourages disease). It also provides the earth with a deep, long drink early on that can help bring your plants through the coming hot afternoon.

Do remember one thing, though: It’s never a good idea to work in your garden when the plants are wet (whether from rainfall or overhead watering). You can easily damage crops at such a time or — worse — spread disease. (Carrots, tomatoes, beans, and squash are especially vulnerable to handspread disease.)

How Often and How Much to Water

Just as you may choose between two generally preferred times to water, there are also two schools of thought on how often to water. Daily light watering regularly replenishes the water that growth and evaporation use up. This way, the soil’s water “arteries” remain intact and reach deep into the ground. And occasional deep watering accomplishes the same goal by periodically drenching the soil thoroughly.

Choose whichever technique you prefer — just DON’T go with occasional light watering. Such half-hearted efforts will keep only the top inch or two of soil moist . . . coaxing roots to grow only near the surface where they can readily dry out.

To make sure you’re watering enough — whether you go for the daily-light or the occasional-deep method — get a trowel, a soil tube, or an auger, and after you’ve watered, dig down about a foot to see just how deep your added moisture is penetrating. This is a very important learning step. With time, you’ll develop a feel for how to keep the soil at its optimum saturation level. But until you gain such expertise, digging to see what’s really happening underground is the way to go (and learn).

The first time or two you check, you may well discover that you’ve been watering too shallowly. Many people make that mistake, failing to realize that it can take three-quarters of an hour to fully water one 10 foot by 10 foot plot! Indeed, the average garden needs about one inch of rain or irrigation per week . . . which figures out to about 62 gallons per 100 square feet. If you provide that much in one weekly watering, it should soak the ground to a depth of about one foot. (Dig and see!)

Of course, most times, natural rainfall will provide some of that moisture, and you’ll only have to make up the difference. You can estimate the amount of natural precipitation you’ve received by following your local weather reports, by putting a large can in the garden and measuring how deep the water in it is after each rain, or — if you like precision — by making your own rain gauge from a funnel and cylindrical tube. For the last method, use a funnel with steep sides, and set it where it’s not exposed to ground splashings or heavy winds (about a foot off the ground is good). You can also add a thin film of oil to the cylinder to reduce evaporation losses. To determine the number of inches of rainwater in the cylinder that will equal one inch of rainfall, divide the squared radius of the funnel by the squared radius of the cylinder. Thus, if your funnel has a three-inch radius and your collecting tube a one-inch radius, every nine (3 ² + 1 ²) inches of water collected in the cylinder will equal one inch of rainfall.

What about droopy leaves? Won’t they tell you that you need to water? Well, not necessarily. Plants often wilt some on a hot summer day as a way of shutting down their systems to conserve moisture. If you water at that time, you can shock the flowers and vegetables and cause more harm than good. (In fact, if you overhead-water on such occasions, the plants may actually lose moisture; the leaves will give up internal liquid to try to balance the perceived atmospheric humidity and end up worse off.)

Instead, look for signs of wilting during morning and evening hours. If the leaves are drooping then, it’s almost a sure sign that your plants need water — and fast! (One exception: Plants can also wilt if their roots are so wet that they’re flooded. A quick trowel-in-the-dirt will determine the true cause if you have any doubts.) Remember, though, that some waxy-leaved plants, such as cabbage, onions, and garlic, don’t show water stress as clearly as others. On the other hand, peas, celery, spinach, and lettuce are very susceptible to drought conditions and will let you know in no uncertain terms!

Garden Watering Tools

A quality garden hose is the heart of any watering system. A hose that will resist its inborn urge to kink and cut off flow is all but priceless. So don’t skimp on this purchase — you’ll never regret it. Standard diameters are 1/2 inches, 5/8 inches, and 3/4 inches. The larger the diameter, of course, the greater the flow. (By the way, if you garden with raised beds, you can set rebar posts — with bamboo or PVC collars — at the corners of your growing areas . . . and the posts will conveniently steer your hose around the beds!)

A watering wand is a hose attachment that consists of along tube with a rose nozzle at the end. It’s kind to your back, allowing you to stand upright while gently but thoroughly soaking the soil at ground level. The wand is just the thing for ground-watering melons, squashes, tomatoes, and other plants susceptible to leaf molds and fungi. It’s also an efficient water user, since it places the liquid right where you want it, rather than spraying it all through the air and garden. We use ours frequently.

There are other common hose attachments for hand-held watering, including the fireman-type nozzle, the spray gun, and fan sprayers. All of these can be useful, but you do have to stand there and hold them . . . which takes time and increases the likelihood that you may skimp on watering. To make your operation a bit more automated, use a rotary or oscillating sprinkler. (The latter is generally easier to use, since most of us lay out our gardens in rectangular — not circular — patterns.) Sprinklers won’t apply water entirely evenly, however, and they need to be moved periodically to prevent spot-flooding and runoff problems. (You can buy automatic timers to shut them off after specified periods.) A good source for sprinklers and other hose attachments is Smith & Hawken, Mill Valley, CA.

Sprinklers have other drawbacks. They waste a lot of water, both by evaporative loss and by wetting pathways — and weeds — as much as crops. They can increase salt buildup in your soil or on your plants (do your crops’ leaves have a powdery residue on them or a burned-edge look?). And they wet the leaves of your disease-susceptible crops.

The most water-efficient, automated system around is drip irrigation — invented when an Israeli engineer by the name of Symcha Blass spotted the beneficial effects of a leaky spigot on the growth of a nearby tree. Drip irrigation systems today come in two types: plastic hoses with small valves — called emitters — spaced every couple of feet, and microporous plastic pipes that weep liquid along their entire length. Both systems use from one-third to one-half less water than do overhead watering methods . . . put the liquid right at your crops’ roots . . . and help increase yields by reducing the stress of extreme fluctuations in moisture levels. Indeed, tests at Ohio State University have shown that peppers and cantaloupes grown with drip irrigation and black plastic mulch produced more than twice the yield of those grown without those two aids.

Drip systems do have some possible drawbacks. Their openings can clog (to avoid that, put an appropriate filter in your waterline). They can start to break down after prolonged exposure to sunlight (that won’t happen if you keep the line just underground). And they must be moved whenever you’re going to do any serious cultivation.

Their biggest disadvantage, at least for people with larger gardens, is cost . . . around $15 to $30 per hundred feet of tubing. Perhaps the best way to deal with that consideration is to buy a small “starter” drip system and try it out for a season so you can evaluate its effectiveness. Indeed, we intend to assess the merits of a number of such systems this summer at the Eco-Village. We’ll tell you what we find out! [EDITOR’S NOTE: And we did! Our article “Ooze Whoin Drip Irrigation” — just last issue — compared six beginning drip kits.]

Water Conservation

Many times, conserving water will be as important as getting some to your crops. Particularly during July or August dry spells, you’ll want to make sure your garden uses and loses as little water as possible.

In a row garden, one of the easiest ways to cut water demand is to plant three to five rows close together and thereby reduce wasted (and watered) pathway space. Of course, gardening in raised beds will save even more space. Since such beds incorporate a greater depth of loosened soil, they also absorb water better than row plantings do. In addition, raised-bed gardening frequently incorporates the art of spacing plants so that their mature leaves just touch — thus creating a “living mulch” that further blocks evaporation and conserves moisture.

Combine raised beds, living mulch, and double-digging (to loosen the soil as deep as possible), and you’ll have a highly efficient water-conserving garden: John Jeavons’ Ecology Action group in Willitts, California, has obtained excellent yields of vegetables using these biodynamic/French intensive techniques and one-eighth the water of conventional gardening!

While you obviously want to establish your garden away from the drip line of trees (their roots practically inhale water), those large plants do have their place as windbreaks. Much more water is lost to evaporation from wind than most of us realize. So you’d do well to utilize any available trees, houses, hedges, or fences to slow down the drying effects of hot summer breezes.

Mulching with dry materials such as hay, straw, wood chips, or even black-and-white newspaper pages most definitely helps protect bare soil from evaporative water loss. Keep in mind, though, that you shouldn’t mulch too early in the growing year, or the covering will retard the warming of your soil. Also, carbon-laden mulches do tie up nitrogen while they’re decomposing, so you should be sure that heavily mulched soil has ample nitrogen. (Fish emulsion, blood meal, cottonseed meal, and well-aged manure are some good nitrogen supplements.)

The Fundamental Point

Finally, always remember that while expensive irrigation systems or conservation strategies will help you save water, the most significant way to conserve moisture is to make soil improvement your top priority. A humus-rich soil — created by using lots of compost and cover crops — will hold the water it gets while still allowing for aeration. Indeed, the soil should be our first concern in all aspects of farming and gardening, because nurturing the diverse life it sustains is the strongest step we can take toward growing healthy plants.

Water-Saving Tricks

There are plenty of small-scale steps you can take to make efficient use of garden water. Here are four no-cost tricks you might try:

1. Don’t stake plants. Let your tomatoes, beans, and other climbers sprawl (on clean, dry mulch), or else grow bush varieties. By doing so, you’ll expose less leaf area to the drying effects of sun and wind.
2. Grow some vegetables in partly shaded areas. Lettuce, parsley, peas, cabbages, and broccoli — among others — can do quite well on just five hours of direct summer sunlight a day. Fine netting shades crops well.
3. Punch small holes in the bottoms of large cans or plastic milk jugs, set the containers next to thirsty plants, and then fill them with water.
4. Hill up the sides of raised beds to create basins that will trap and hold as much rainwater as possible.

Originally published as “Watering the Garden” in the July/August 1986 MOTHER EARTH NEWS NO. 94 issue.